The Immunizing Value of Acetone- and Heat-Killed Vaccines *

Vaccines prepared in various ways have been employed in the study of immunological reactions. Heat-killed vaccines, because of their safety and ease of preparation, have received wide attention, but such vaccines in the study of immunity in mouse typhoid produced with B. enteritidis have not given the degree of resistance desired. Studies of certain types demand the use of a killed vaccine, and one which will produce an immunity in a large percentage of animals. The agent used in killing the bacteria thus becomes a matter of importance. Wadsworth and his co-workers8'9 have shown that two volumes of acetone do not degrade the antigenicity of streptococcus toxin or diphtheria toxoid. In studying the immunizing power of various fractions of B. aertrycke Raistrick and Topley6 used as a standard for comparison an acetone-killed B. aertrycke vaccine. This vaccine produced a definite immunity, although only one injection (sometimes two) was given. Alcohol was a means of sterilizing the sensitized typhoid vaccines of Gay and others3. To test the relative value of immunity obtained with B. enteritidis vaccines sterilized by heat, acetone, and alcohol, the following preparations were made. A virulent strain of B. enteritidis 904 of the American Type Culture Collection was grown on a yeast extract (Savita) agar (pH 6.9) at 370 C. for 18 hours. The growth from 22 Roux bottles was washed with saline, centrifuged, and washed again with saline. After resuspending in physiological salt solution the organisms were divided into three equal portions. One portion was heated in a water-bath at 60° C. for one hour. This was called 60° C. heat-killed vaccine. The sediment of the second portion, following centrifuging for one hour, was suspended in 50 per cent C.P. acetone in distilled water and allowed to stand for 45 minutes, shaking occasionally. This mixture was centrifuged, the sediment washed and resuspended in saline, and labelled 50 per cent acetonekilled vaccine. The third portion was treated in the same manner